In combustion engines, when the inlet valves are opened, residual gas flows back into the intake duct. The fresh air to fill the cylinder thus contains a certain proportion of residual gas, which has to be taken into consideration when calculating the fresh air mass.
DE 198 44 085 C1 discloses a method for controlling an internal combustion engine as a function of an exhaust gas pressure. The method includes the step of calculating, with the aid of a model, an induction manifold pressure in the intake duct and the air mass flow into a cylinder. A correction factor is provided for the mean exhaust gas pressure during valve overlap, and is dependent on a center of gravity angle of the valve overlap.
EP 1 030 042 A2 discloses a method of determining cylinder filling of an engine without throttle. This method takes account of the fact that the residual gas pushed back into the inlet duct in front of the upper dead point is taken in again only after the intake operation. Assuming a so-called stopper model, the intake valve surface situated in front of the upper dead center is doubled and subtracted from the maximal valve opening surface.